Zoho Creator lets you build your own simple web application in a few simple steps.

With Zoho Creator, you can create your own application, copy and tweak someone else's, and share it with the world. Zoho Creator is very similar to previously-mentioned web app builder Ning, though the interface looks nicer, and the apps I've checked out on Zoho Creator seem more robust (the Project Tracker demo is pretty impressive). If you give it a try, let us know what you think in the comments or at tips at lifehacker.com.